Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, stations (STAs), wireless devices, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a wireless communications network, such as a cellular communications network sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB, micro eNode B or pico base station, based on transmission power, functional capabilities and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Finding the accurate position of one or more UEs located in one or more indoor areas for different applications, such as emergency situations, is among one of the studies of 3GPP Release-13. The objective is to study techniques for indoor positioning. The positioning technique and/or positioning system may be Radio Access Technology (RAT) dependent or RAT independent. Some examples of RAT dependent positioning techniques are based on or comprise the use of Observed Time Difference of Arrival (OTDOA), Uplink Time Difference Of Arrival (UTDOA), Enhanced Cell ID (E-CID), Radio Frequency Pattern Matching (RFPM), etc. Some examples of RAT independent positioning techniques are based on or comprise the use of Assisted Global Navigation Satellite System (A-GNSS), Terrestrial Beacon Systems, etc. For indoor UEs, i.e. for one or more UEs located in an indoor environment, their vertical positioning, i.e. the altitude, may also be a useful parameter to be considered, e.g. when the UEs are present in a building with multiple floors.
FIG. 1 illustrates an exemplifying positioning architecture according to prior art. In FIG. 1 a 3GPP LTE and Evolved Packet Core (EPC) communications network 100 is schematically illustrated. An Evolved Serving Mobile Location Center (E-SMLC) 102 supports a UE 104 as well as the network 100 in order to derive an estimate of the position of the UE 104 or of a network node, e.g. an eNB 106. Exemplary use cases comprise emergency use case where emergency calls must be positioned, as well as commercial use cases wherein either the UE 104 or the network 100 benefits from determining the position of the UE 104. The E-SMLC 102 interacts with the UE 104 via an LTE Positioning Protocol (LPP) that may be routed via the control plane or the user plane. Furthermore, the E-SMLC 102 interacts with the eNB 106 via the LPPa protocol. In the latter case, the eNB 106 may interact with the UE 104 via a Radio Resource Control (RRC) message to request information needed for positioning. Examples of such information are radio condition measurements, timing information etc. A typical use of the LPPa protocol is to convey the identity of the serving cell to the E-SMLC 102. The E-SMLC 102 may be seen as an exemplifying Position Determining Entity (PDE), but it may also forward obtained information via the LPP and/or the LPPa protocol to a separate PDE.
In LTE, positioning techniques based on or comprising an enhanced Cell ID, an Assisted Global Navigation Satellite System, an Observed Time Difference of Arrival and/or an Uplink TDOA are considered.
In positioning techniques comprising the enhanced Cell ID, essentially cell ID information is used to associate the UE to the serving area of a serving cell. Further, additional information may be used to determine a finer granularity position.
In positioning techniques comprising the Assisted Global Navigation Satellite System (GNSS), GNSS information is retrieved by the UE and supported by assistance information provided to the UE from the E-SMLC.
In the positioning techniques comprising the Observed Time Difference of Arrival (OTDOA), the UE estimates the time difference of reference signals from different base stations and either sends the estimated time difference to the E-SMLC for multilateration or alternatively the multilateration for position estimation is done by the UE based on assisted information from the E-SMLC.
In the positioning techniques comprising the Uplink TDOA (UTDOA), the UE is requested to transmit a specific waveform that is detected by multiple location measurement units, such as one or more Radio Network Nodes e.g. one or more eNBs, at known positions. These measurements are forwarded to the E-SMLC for multilateration.
Multilateration (MLAT) is a navigation technique based on the measurement of the difference in distance to two stations at known locations that broadcast signals at known times. Unlike measurements of absolute distance or angle, measuring the difference in distance between two stations results in an infinite, e.g. a huge, number of locations that satisfy the first measurement. When these possible locations are plotted, they form a first hyperbolic curve. To locate the exact location along that curve, multilateration relies on multiple measurements: a second measurement taken to a different pair of stations will produce a second hyperbolic curve, which intersects with the first hyperbolic curve. When the two curves are compared, a small number of possible locations are revealed.
Due to the significant amount of path loss in indoor scenarios, e.g. indoor environments, using the existing positioning techniques for accurate indoor positioning estimation may become challenging. Another problem with estimating a position of a UE located inside, e.g. within, an indoor area, is the existence of different floors, e.g. storeys, in the building. Therefore, the vertical accuracy of the position of the UE in the indoor area will also become a challenge, and the performance of the existing positioning techniques for the vertical positioning is still an open area to be studied.